Mass flow controller

ABSTRACT

A mass flow controller has a sensor section that generates an electrical signal, dependent on the measured flow rate. The controller sends a control signal to a magnetic field generating unit, dependent upon the actual flow rate and the desired flow rate, which in response, generates a magnetic flux in the direction of the fluid input to the fluid output through the body of the controller. This means that the magnetic flux is concurrent with the fluid flow within the mass flow controller body. The magnetic flux alters the position of a plunger button assembly, located between the bypass chamber and the fluid output, relative to an orifice plate to control the flow rate to obtain the desired output flow. By incorporating the proportional control valve within the mass flow controller body, the need for a separate and large valve section is eliminated, reducing the size and cost of the controller.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This is a continuation-in-part application of commonly-owned U.S.patent application Ser. No. 09/517,391, filed Mar. 2, 2000.

FIELD OF THE INVENTION

[0002] The present invention relates to mass flow controllers.

[0003] 1. Description of Related Art

[0004] Mass flow controllers are known in the art for controlling thespecific amount of flow of a fluid, necessary for a particular process,e.g., in semiconductor manufacturing processes, such as chemical vapordeposition or the like. Mass flow controllers are known to be capable ofsensing the flow occurring through the controller and modifying orcontrolling that flow as necessary to achieve the required control ofthe mass of the fluid delivered to the particular process.

[0005] Sensing the flow is a function of the type of fluid utilized andthe physical effect used to sense the amount of flow. One typical typeof physical effect to sense mass flow is to measure the temperaturedifferential between the upstream and downstream heater/sensor coilsexposed to the fluid flow. Other systems may use absolute and/ordifferential pressure changes, light absorption, or the momentum change(e.g., paddle wheel) to measure the flow.

[0006] Modifying or controlling the flow is typically made in responseto the sensed flow as it relates to the desired flow by modifying across-sectional opening area available to the fluid for flowing. Thesmaller the area available for flow, the smaller the mass flow, andvice-versa. In the past, this has been accomplished with a typicalplunger/diaphragm/orifice system. An orifice provides the variable crosssectional opening area for flow, where the flow control is dictated bythe positioning and motion of a plunger/diaphragm or needle stem in theorifice in response to a flow control signal. The flow control signal isgenerated in response to the measurement of the flow sensor.

[0007] A servo control section generates a control signal that drivesthe positioning of the plunger/diaphragm or needle stem, typicallythrough the use of a solenoid type of driver. The solenoid driver has aferromagnetic core surrounded by a coil. The plunger/diaphragm,typically made of ferromagnetic material, is held close to the orificeby a spring. The energizing of the coil generates a magnetic field thatpulls the plunger/diaphragm away from the orifice while the spring pullsit toward the orifice. The distance between the orifice and theplunger/diaphragm is dependent upon the relative strengths of themagnetic field and the spring. The proportional control valve by itsnature is not an open and shut valve. The closer the needle stem orplunger/diaphragm is to the orifice, the more restricted the flowbecomes, until the flow is shut off, and the more it is withdrawn themore the flow increases, until it no longer affects the amount of flow.

[0008] For precision control, complex and expensive controller circuitryis needed to control the positioning and movement of the needle stem orplunger/diaphragm as the flow is regulated. The valve parts themselvesmust be manufactured with high precision, and are therefore expensive.In addition, prior art proportional controlled solenoid valve mass flowcontrollers require the needle stem or plunger/diaphragm to be mountedat right angles to the fluid flow direction. Consequently, the orificeis also mounted at right angles to the fluid flow path, and the fluidhas to change direction to go through the orifice, which generatesturbulence in the fluid.

[0009] Often the mass flow controller, particularly when used in highprecision semiconductor manufacturing processes and the like, is part ofa tool that has limited space available for the flow controllers,particularly if there are multiple mass flow controllers that arepositioned in the immediate area of the actual discharge of the fluidinto the tool's process chamber.

[0010] There is a need in the art, therefore, for a mass flow controllerthat is simpler, less expensive, smaller, and easier to manufacture andcontrol.

SUMMARY OF THE INVENTION

[0011] The present invention, according to one embodiment, utilizes aclosed loop magnetic flux path passing through the body of thecontroller in the direction of flow from its input to its output tomagnetically operate a flexible plunger button valve assembly that isnormally spring biased into the shut position. A current generated froma servo control section of a mass flow controller generates magneticflux to pull the plunger valve assembly away from an orifice and allowmore fluid to flow through. By controlling the amount of flux generated,and thereby the positioning of the button valve assembly relative to theorifice, the flow through the orifice can be controlled. Consequently, alarge separate proportional control valve section is no longernecessary, which results in a more compact, less expensive and morereliable mass flow controller that is less costly to manufacture and hasfewer components than the conventional mass flow controllers discussedabove.

[0012] The present invention will be more fully understood uponconsideration of the detailed description below, taken together with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013]FIG. 1A shows a mass flow controller of the prior art;

[0014]FIG. 1B shows magnetic flux path through a mass flow controller ofFIG. 1A;

[0015]FIG. 2 shows an exploded view of the mass flow controller of FIG.1A;

[0016]FIG. 3A shows a mass flow controller according to one embodimentof the present invention;

[0017]FIG. 3B shows a bypass assembly of FIG. 3A according to oneembodiment;

[0018] FIGS. 3C-3G show various embodiments of a bypass assembly;

[0019]FIG. 3H shows magnetic flux path through a mass flow controller ofFIG. 3A;

[0020]FIG. 4 shows an exploded view of the mass flow controller of FIG.3A;

[0021]FIG. 5 shows a sectional view of the mass flow controller of FIG.3A along sectional line A-A′;

[0022]FIG. 6A shows a side view of the button assembly and orifice plateshown in FIGS. 3A and 4;

[0023]FIG. 6B shows a side view of the button assembly and orifice plateaccording to another embodiment;

[0024]FIGS. 7A and 7B show different configurations of an orifice plate;and

[0025]FIG. 7C shows a side view of an orifice plate and button plungerassembly;

[0026]FIG. 8 shows an exploded view of a mass flow controller accordingto another embodiment of the present invention;

[0027]FIG. 9 shows magnetic flux path through a mass flow controlleraccording to another embodiment of the present invention;

[0028]FIG. 10 shows magnetic flux path through a mass flow controlleraccording to yet another embodiment of the present invention;

[0029]FIG. 11 shows a mass flow controller according to anotherembodiment of the present invention;

[0030]FIG. 12 shows the mass flow controller of FIG. 11, rotated 90°about the vertical axis;

[0031]FIG. 13 shows the mass flow controller of FIG. 11 with securingscrews;

[0032]FIG. 14 shows an exploded view of a portion of the mass flowcontroller of FIG. 11, rotated 90° about the axis perpendicular to thevertical axis;

[0033]FIGS. 15 and 16 show a portion of the bypass assembly according totwo embodiments of the present invention;

[0034]FIG. 17 shows a plunger button assembly according to oneembodiment;

[0035]FIG. 18 shows an orifice plate according to one embodiment; and

[0036]FIG. 19 shows the magnetic flux path through the mass flowcontroller of FIGS. 11 and 12.

[0037] Use of the same reference symbols in different figures indicatessimilar or identical items.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0038]FIGS. 1A and 2 show a conventional mass flow controller 10. FIG.1A shows an assembled controller 10, while FIG. 2 shows an exploded viewof parts of controller 10. Mass flow controller 10 has three mainsections: a sensor section 20, a valve section 30, and a mass controllerblock section 40. A fluid input fitting 11 and a fluid output fitting 12are sealed to respective input and output ends of block section 40through metal O-rings 13. Note that other seals are also suitable, suchas knife edge, O-ring, C-ring, and flat gasket, made of materials suchas metal, polymer, and elastomer. A cover 14 enclosing sensor section 20and valve section 30 is secured to input and output fittings 11 and 12by screws 15.

[0039] Gas or fluid enters input fitting 11 through an opening 16 ininput fitting 11. The flow of fluid through mass flow controller 10 isshown in the dark lines in FIG. 1A. Opening 16 opens into a bypassassembly 17, which has an input plenum 18 and an output plenum 19, andwhich is located within block section 40. Sensor section 20 is securedto block section 40 via appropriate seals 22. While a majority of thefluid passes along bypass assembly 17, a portion of the fluid travelsthrough sensor section 20 along a sensor tube 23. Bypass assembly 17restricts the flow of fluid along one of a plurality of channels orgrooves formed in the generally cylindrical outer surface of bypassassembly 17 and into output plenum 19. As is known in the art, this isfor the purpose of generating a laminar flow such that a portion of thefluid passing from input plenum 18 into a sensor bypass line 21 and intosensor portion 20 is linearly proportional to the fluid passing frominput plenum 18 to output plenum 19 through the plurality of channels orgrooves in bypass assembly 17.

[0040] Sensor section 20 typically includes multiple coils 24 wrappedaround sensor tube 23. When fluid flows inside sensor tube 23 from aheated upstream coil to a heated downstream coil that are electricallybalanced, thermal energy is transferred from the coils to the flowingfluid. The amount of thermal energy transferred from the coils to thefluid is inversely proportional to the fluid temperature. Thermal energytransfer from the upstream coil and the downstream coil to the fluid isdisproportionate because the fluid temperature is different at theupstream coil than at the downstream coil. This difference in heattransfer from the upstream coil and the downstream coil results in atemperature differential between the coils which manifests as a changein the relative resistance of the two coils. This change in resistanceis directly proportional to the amount of fluid flowing through sensortube 23. Typically, a resistor circuit (not shown), which is coupled tothe upstream and downstream coils, is configured to form a balancedbridge network when there is no fluid flow. When the fluid flows, theresistance in the coils changes. The bridge network measures the changeof the resistance in the coils and generates a signal corresponding tothe flow of fluid through sensor tube 23.

[0041] Fluid from bypass assembly 17 and sensor tube 23 converge andflow into a fluid flow path 25. Fluid travels along fluid flow path 25,through valve section 30, and out through an opening 26 in outputfitting 12. Valve section 30 includes an upper housing 31 enclosing awound coil assembly 32 of a solenoid valve, which consists of a poleassembly or plug 33. Pole assembly 33 has a lower housing 34, whichtogether with upper housing 31, are secured to block section 40 andsealed with an O-ring 35 or other appropriate seal. A plunger buttonassembly 37, having a flat sealing surface 46, is held in a cavity inlower housing 34 of pole assembly 33 by a plunger button capture ring36. Plunger button capture ring 36, plunger button assembly 37, and aplunger button assembly pre-tensioning ring 38 are in abutting relationto an orifice plate 39, which is sealed to block portion 40 by an O-ring41 or other appropriate seal.

[0042] Orifice plate 39 has an opening 42 into which fluid flows fromfluid flow path 25, where the flow of the fluid is controlled by theposition of the plunger button assembly 37, relative to orifice opening42. The relative position of plunger button assembly 37 is controlled bymagnetic flux generated in core 33 in response to the signal generatedfrom sensor block 20. Coil 32 is held in place by a top cap 43 and apole nut 44. Top cap 43 is sealed with an O-ring 45. FIG. 1B shows themagnetic flux path of controller 10. As seen from FIG. 1B, the magneticflux only travels through valve section 30 to control the position ofplunger button assembly 37, and not through either sensor section 20,bypass assembly 17, or block 40.

[0043]FIGS. 3A and 4 show a mass flow controller 300 according to oneembodiment of the present invention. FIG. 3A shows an assembledcontroller 300, while FIG. 4 shows an exploded view of parts ofcontroller 300. Mass flow controller 300 includes an input fitting 311attached to an input magnetic flux plate 312, typically made offerromagnetic material, where both input fitting 311 and input magneticflux plate 312 have an opening 313 through which fluid enters and anoutput fitting 314 attached to an output magnetic flux plate 315,typically made of ferromagnetic material, where both output fitting 314and output magnetic flux plate 315 have an opening 316 through whichfluid exits. A mass controller block 320, typically made ofnon-ferromagnetic material, is sealed between input magnetic flux plate312 and output magnetic flux plate 315 by O-rings 321 or otherappropriate seals, which can be metal, plated metal, polymeric, orelastomeric material.

[0044] Fluid flows through opening 313 into a bypass assembly 317,typically formed with a ferromagnetic material, via distribution holes318. Bypass assembly 317 can be a single part with longitudinal groovesor channels 350 formed directly thereon, or in other embodiments, bypassassembly can be formed from more than one part, as shown in FIG. 3B. Forexample, bypass assembly 317 can be formed from an inner core 355 and anouter sleeve 360 having grooves 350 formed along the outer perimeter.Inner core 355 can be of a ferromagnetic material, while outer sleeve360 can be of a non-magnetic material. In another embodiment, inner core355 is made of a non-magnetic material, and outer sleeve 360 is made ofa ferromagnetic material.

[0045] Other embodiments of bypass assembly 317 are shown in FIGS.3C-3G. In each of these embodiments, a bypass assembly 317 includes aferromagnetic core and pathways along the longitudinal direction of thebypass assembly that allow fluid to flow from one end of the assembly tothe other. In FIG. 3C, ferromagnetic core 355 is surrounded byconcentric tubes 361 held in place by ribs 362. Fluid flows alongchannels created by concentric tubes 361 and ribs 363. In FIG. 3D,ferromagnetic core 355 is surrounded by longitudinal tubes 363 in one ormore layers, enclosed by a non-magnetic body 364. Fluid flows throughtubes 363. In FIG. 3E, ferromagnetic core 355 is surrounded by one ormore laminated sheets 365 having channels 366, which can be formed bylaminating a channeled sheet 367 to a flat sheet 368. Laminated sheet365 is then wound around ferromagnetic core 355. Additional sheets canbe wound around an inner sheet to provide multiple channels throughwhich fluid can flow. In FIG. 3F, ferromagnetic core 355 is surroundedby a porous material 369, which allows fluid to flow through. In FIG.3G, core 355 is made of a ferromagnetic porous (sintered) material.Thus, core 355 functions as the path for both the magnetic flux as wellas the fluid flow through bypass assembly 317.

[0046] Going back to the embodiment of FIG. 3B, the fluid flows alonglongitudinal flow groves along the outer circumference of bypassassembly 317. Fluid also flows through distribution holes 318 to a flowsensor input line 319 formed within block 320. Input line 319 directsthe flow to a sensor unit 322, which is secured to block 320 by screws323 and two O-rings 324 or other appropriate seals. One O-ring 324 sealsthe interface between sensor unit 322 and input line 319 of block 320and second O-ring 324 seals the interface between sensor unit 322 and anoutput line 325 formed within block 320. Fluid from output line 325 andbypass assembly 317 travels through a plunger button assembly capturespacer 326, typically made of ferromagnetic material, a plunger buttonassembly 327, (which includes a plunger made of ferromagnetic material,a spring, and a sealing surface), a plunger button pre-tension spacer328, an orifice plate 329 typically made of non-magnetic material, andan orifice metal O-ring 330 or other seal, and out through opening 316in output fitting 314. Plunger button assembly 327 and orifice plate 329are shown in greater detail in FIG. 6A. Plunger button assembly capturespacer 326 secures plunger button assembly 327, spacer 328, orificeplate 329, and O-ring 330 within a cavity in output magnetic flux plate315.

[0047] In addition, mass flow controller 300 of the present inventionincludes a magnetic field generating unit 340. Magnetic field generatingunit 340 includes a coil 341 and a core 342 inserted into a cylindricalopening within coil 341. Core 342 is a cylindrical plug, typically madeof a ferromagnetic material, which is inserted into openings in theupper portion of input magnetic flux plate 312 and output magnetic fluxplate 315. Magnetic flux generated by unit 340 is directed down throughinput magnetic flux plate 312, to bypass assembly 317, to plunger buttonassembly 327, and back up through output magnetic flux plate 315. FIG.3H shows the magnetic flux path of controller 300. As seen in FIG. 3H,the magnetic flux travels substantially with the fluid flow within thebody of controller 300, i.e., from input magnetic flux plate 312 andthrough bypass assembly 317 to output magnetic flux plate 315. This iscontrasted with the magnetic flux path of conventional controllers, suchas shown in FIG. 1B.

[0048]FIG. 5 is a sectional view of mass flow controller 300 alongsectional line A-A′ of FIG. 3A. FIG. 5 shows that sensor unit 322 isrotated approximately 90° from the orientation of conventional mass flowcontroller 10 shown in FIGS. 1A and 2. In other words, fluid flowingthrough sensor unit 322 is orthogonal to the flow direction of the fluidthrough bypass assembly 317 according to the present invention, whereasthe flow directions are parallel with the controller shown in FIGS. 1Aand 2. Sensor unit 322 is a conventionally known and used thermal massflow sensor. The majority of the fluid flows through bypass assembly 317along flow grooves 350 formed longitudinally on the outer surface ofbypass assembly 317. Some of the fluid flows from distribution holes 318to flow sensor input line 319 and into a flow sensor tube 344. Sensortube 344 has wrapped around its outside a first heater/sensor coil 345and a second heater/sensor coil 346, which are connected to terminals347.

[0049] Passing current through first coil 345 heats the fluid as itpasses through sensor tube 344 in the vicinity of first coil 345.Current is also passed through second coil 346 wrapped around sensortube 344 in the downstream flow direction of the fluid, i.e., towardsoutput line 325. As the fluid passes second coil 346, it gets hotter.However, the amount of heat transferred from coils 345 and 346 to thefluid is different because the fluid temperature is different at coils345 and 346. This in turn changes the relative resistance of coils 345and 346, which is measured as a voltage differential in an electricalbridge (i.e., a Wheatstone bridge). This voltage differentialcorresponds to the mass flow amount of fluid passing through sensor tube344, and, proportionately, through bypass assembly 317. Controller unit300 includes electronic circuitry, not shown, to calculate the mass flowbased upon the sensed change in voltage. A servo control section ofcontroller 300 then generates a current signal for magnetic fieldgenerating unit 340, which in turn generates magnetic flux proportionalto the signal to move plunger button assembly 327 to control the flow.The servo control system generates current through the coil to generatesufficient magnetic flux until the error signal is minimized orapproximately zero. Such systems are conventional and known to thoseskilled in the art.

[0050]FIG. 6A shows, in more detail, plunger button assembly 327 andorifice plate 329 according to one embodiment. Orifice plate 329 isgenerally flat on both faces, with the face toward button assembly 327having a frusto-conical portion 600. Frusto-conical portion 600 has anopening 610 extending through orifice plate 329 such that fluid can flowthrough orifice plate 329 to opening 316 in output fitting 314. Plungerbutton assembly 327 has a smooth flat sealing surface 620 that sits onto frusto-conical portion 600. Plunger button assembly 327 also hasopenings 331 located outside sealing surface 620 for fluid to passthrough. A spacer 328 (shown in FIG. 4) is positioned between plungerbutton assembly 327 and orifice plate 329. Spacer 328 is intended forthe purpose of creating an appropriate amount of compression betweenplunger button assembly 327 and frusto-conical portion 600 by allowing aspring 625 in plunger button assembly 327 to bend to a desired extent byplunger button assembly capture spacer 326. The thinner the spacer 328,the greater the bending of spring 625 in plunger button assembly 327,consequently creating greater compression between plunger buttonassembly 327 and frusto-conical portion 600.

[0051] Fluid flows through openings 331 around the outer edges ofsurface 620 as well as around the outer edges of plunger button assembly327 so that fluid can flow from bypass assembly 317 to opening 610 oforifice plate 329. The amount of fluid flowing into opening 610 dependson the positioning of plunger button assembly 327 in relation to orificeplate 329. As the attractive force to plunger button assembly 327, whichis created by the magnetic flux, increases, plunger button assembly 327is moved away from orifice plate 329, thereby increasing the amount offluid flowing into opening 610. However, as the force decreases, thespring pushes button assembly 327 towards orifice plate 329, therebydecreasing the fluid flow into opening 610. The spring force of thespring should be as small as possible, yet sufficient to seal opening610 to give a zero flow through opening 610. Zero flow means less than0.5% of the mass flow controller range.

[0052]FIG. 6B shows another embodiment of plunger button assembly 327 inwhich a magnet 626 is attached to the side of plunger button assemblyopposite sealing surface 620. By changing the flux direction andmagnitude through bypass assembly 317, plunger button assembly 327 canbe moved either away from or towards orifice plate 329, therebycontrolling the flow of fluid through orifice plate 329. For example, ifthe magnetic flux creates a pole on the end of bypass assembly 317 thatis opposite in polarity to magnet 626, the attractive force betweenbypass assembly 317 and plunger button assembly 327 (via magnet 626)will pull plunger button assembly 327 away from orifice plate 329, whichallows fluid to flow. If the magnetic flux creates a pole that is thesame in polarity as magnet 626, bypass assembly 317 will force plungerbutton assembly 327 into orifice plate 329, which will shut off thefluid flow. Thus, depending on the magnitude and direction of the fluxand the strength of magnet 626, a desired fluid flow can be obtained.

[0053] In the above described embodiments, opening 610 in orifice plate329 is a central through hole. However, in other embodiments, opening610 can be an annular ring of slots 700 (shown in FIG. 7A) or holes 710(shown in FIG. 7B), or a combination of both. In these embodiments, theannular ring of holes or slots extend through protruded portions 720 oforifice plate 329, shown in FIG. 7C. Plunger button assembly 327 has acentral hole 730 or slots (not shown) and sealing surface 740, whichabuts against protruded portions 720 of orifice plate 329. Without anymagnetic flux, protruded portions 720 are sealed against sealing surface740, thereby preventing fluid from flowing through the holes or slots inorifice plate 329. When magnetic flux is generated, plunger buttonassembly 327 is pulled away from orifice plate 329 to allow fluid flowthrough orifice plate 329. Fluid flows through hole 730 of plungerbutton assembly 327 and holes or slots 750 on the outer edge of sealingsurface 740 as well as from the outer perimeter of plunger buttonassembly 327 to the openings of orifice plate 329.

[0054] The size and number of slots 700 or holes 710 can be chosen tomake the mass flow controller for a desired flow rate. For a given flowrate, the area of the slots (FIG. 7A) or holes (FIG. 7B) should beminimized to reduce the back pressure, resulting in less force required(less magnetic flux and therefore less current required) to move plungerbutton assembly 327. However, this area must not be minimized to theextent that choking occurs when fluid is attempting to pass throughorifice plate 329. Choking can also occur in the peripheral area of theslots or holes. Therefore, the peripheral area of the slots or holesshould be greater than or equal to the cross-sectional area of the slotsor holes. Referring to FIGS. 7A-7C, the peripheral area can be definedas the perimeter of the slots or holes times a displacement distance d.Distance d is the maximum distance between plunger button assembly 327and the end of protruded portions 720 for a given flow rate, as shown inFIG. 7C.

[0055] Therefore, for a given flow rate and cross-sectional area ofslots 700, the peripheral area of the slots can be made equal to orgreater than the cross-sectional area of the slots by either increasingthe perimeter of the slots or increasing the distance d. Increasingdistance d requires more magnetic force to achieve the desired flowrate. On the other hand, increasing the perimeter of the slots, whichcan be done by increasing the length of the slots and decreasing thewidth of the slots, allows the peripheral area of the slots to beincreased without changing the cross-sectional area of the slots.Consequently, the back pressure is not adversely increased or affected.However, the same effect cannot be realized by using holes instead ofslots because increasing the perimeter or circumference of the holesalso increases the cross-sectional area of the holes.

[0056]FIG. 8 shows another embodiment of the present invention, in whichbypass assembly 317 is made of a magneto-restrictive material, insteadof a ferromagnetic material described above. The end of bypass assembly317 facing output magnetic flux plate 315 is secured to a sealing device800 having holes 805 for fluid to flow through and a sealing area 810that abuts orifice plate 329 to prevent fluid from flowing throughopening 610 in orifice plate 329. In the normal biased position, sealingdevice 800 abuts orifice plate 329 when sufficient magnetic flux isgenerated to seal opening 610. Magnetic flux travels from input magneticflux plate 312 toward output magnetic flux plate 315 through bypassassembly 317 and sealing device 800. When the magnetic flux is reduced,the magneto-restrictive material constricts, which allows fluid to flowthrough opening 610 in orifice plate 329. Then, when the magnetic fluxis increased, bypass assembly 317 expands until sealing device 800 sealsopening 610. This allows plunger button assembly 327 and plunger buttonassembly pre-tension spacer 328 of FIG. 4 to be eliminated.

[0057] In the above described embodiments, the magnetic flux travelsthrough bypass assembly 317. In other embodiments, shown in FIGS. 9 and10, the magnetic flux path travels through the body of the mass flowcontroller. In FIG. 9, the magnetic flux path (shown as a solid blackline) travels through core 342, along input magnetic flux plate 312,through mass controller block 320, which in this embodiment is typicallymade of a ferromagnetic material, through plunger button assembly 327and back up through output magnetic flux plate 315. A magnetic fluxseparator plate or washer 910, typically made of a non-magneticmaterial, is located between mass controller block 320 and outputmagnetic flux plate 315 so that the magnetic flux travels throughplunger button assembly 327 to control the fluid flow through orificeplate 329. In FIG. 10, coil 341 is wound around mass controller block320. Mass controller block 320, typically made of a ferromagneticmaterial, encloses bypass assembly 317. An outer cover 100, typicallymade of a ferromagnetic material, encloses coil 341 and block 320.Similar to FIG. 9, magnetic flux separator plate or washer 910 separatesmass controller block 320 from output magnetic flux plate 315.Accordingly, as shown in FIG. 10, the generated magnetic flux (shown asa solid black line) travels through block 320 to plunger button assembly327, up through output magnetic flux plate 315, along outer cover 100,and down through input magnetic flux plate 312. Note that in theembodiments shown in FIGS. 9 and 10, fluid flows through sensor section20 (FIGS. 1A and 1B) parallel to the flow of fluid through bypassassembly 317. However, the embodiments shown in FIGS. 9 and 10 are alsosuitable with sensor unit 322 (FIGS. 3A and 5) that allows fluid to flowperpendicular to the flow of fluid through bypass assembly 317.

[0058] FIGS. 11-19 show an assembled mass flow controller 920 accordingto another embodiment of the present invention, with FIG. 14 showing anexploded view of parts of mass flow controller 920, rotated 90°, fromFIG. 11. Referring to FIGS. 11 and 14, mass flow controller 920 hasthree main sections: a controller block section 921, a bypass/valvesection 922, and a sensor section 923. Bypass/valve section 922 with asolenoid core 924 and a solenoid coil 925 are contained within blocksection 921. A cover 926 encloses an electronic control printed circuitboard (PCB) 927 and sensor section 923. Mass flow controller 920 isattached and sealed to a surface mount block, such as by screws 928(FIG. 13) and fluid input/output seals 929.

[0059] Referring to FIG. 11, fluid enters through an input port 930 andflows through a channel 931 into an input plenum 932 located withinblock 921, which is typically made of a non-ferromagnetic material.There, the fluid is split, with a majority of the fluid flowing alonglongitudinal grooves/channels 933 (FIGS. 14-16) formed in the generallycylindrical outer surface of a bypass/valve body 934, typically madefrom a ferromagnetic material. In various embodiments, grooves/channels933 can be formed directly on bypass/valve body 934 (FIG. 14), on asleeve 935 (FIG. 15), within a sleeve when the sleeve is a porousmaterial that acts as grooves/channels 933, or on the inner surface ofblock 921 (FIG. 16). Bypass/valve assembly 922, which includesbypass/valve body 934, is attached to block 921, such as by screws 936(FIG. 13) and seals 937 and 967 (FIGS. 11 and 14). Thus, in bypass/valveassembly 922 within block 921, the fluid flows from fluid input port 930to fluid input plenum 932 to an output plenum 938.

[0060] Referring to FIGS. 11-14 and 19, sensor section 923 is attachedto bypass/valve assembly 922, such as by screws 939 and seals 940, andcan be mounted in any 360° orientation substantially perpendicular tothe flux path, as shown in FIG. 19. Sensor section 923 includesconventionally known and used thermal mass flow sensors. Referring toFIG. 12, the smaller portion of the split fluid flows through channel941 located within bypass/valve body 934 into a sensor tube 942 andexits from sensor tube 942 into channel 943 located in bypass/valve body934 and flows through channel 944 located within block 921, finallymeeting the major portion of the split fluid at the output end of thebypass/valve assembly 922 at output plenum 938. Sensor tube 942 haswrapped around its outside a first heater/sensor coil 945 and connectedto terminals 946.

[0061] Passing current through first coil 945 heats the fluid as itpasses through sensor tube 942 in the vicinity of first coil 945.Current is also passed through a second coil 947 wrapped around sensortube 942 in the downstream flow direction of the fluid, i.e., towardschannel 943. As the fluid passes second coil 947, it gets hotter.However, the amount of heat transferred from coils 945 and 947 to thefluid is different because the fluid temperature is different at coils945 and 947. This in turn changes the relative resistance of coils 945and 947, which is measured as a voltage differential in an electricalbridge (e.g., a Wheatstone bridge). This voltage differentialcorresponds to the mass flow amount of fluid passing through sensor tube942, and proportionally through bypass/valve assembly 922. Mass flowcontroller 920 includes electronic control PCB 927 to calculate the massflow based upon the sensed change in voltage.

[0062] Bypass/valve assembly 922 contains core 924, typically made froma ferromagnetic material, surrounded by solenoid coil 925. One end ofcore 924 is in intimate contact with a valve pole 948, typically madefrom a ferromagnetic material. The other end of core 924 is in intimatecontact with a solenoid cap 949, typically made from a ferromagneticmaterial. Cap 949, in turn, is in intimate contact with bypass/valvebody 934. Valve pole 948 is separated from bypass/valve body 934 by aflux isolation ring 950, typically made from a non-ferromagneticmaterial.

[0063] An electronic servo control section on PCB 927 generates acurrent signal (depending upon the actual flow and the desired flow) forsolenoid coil 925, which in turn generates magnetic flux proportional tothe signal to move a plunger button assembly 951 (shown in greaterdetail in FIG. 17) to control the flow, as discussed in more detailbelow. The servo control system generates current through coil 925 togenerate sufficient magnetic flux until the error signal (differencebetween the desired flow and actual flow) is minimized or approximatelyzero.

[0064] An orifice plate 952, as shown in FIG. 18, typically made of nonferromagnetic material, is generally flat on both faces, with the facetowards plunger button assembly 951 having a frusto-conical portion 953.Frusto-conical portion 953 has an opening 954 extending through orificeplate 952, such that fluid can flow through orifice plate 952 to a fluidoutput channel 955 into an output port 956. Plunger button assembly 951,as shown in FIG. 17, has a smooth flat sealing surface 957 that sits onto frusto-conical portion 953. A spring pretension spacer 958 ispositioned between plunger button assembly 951 and orifice plate 952, asshown in FIGS. 11 and 14. Spacer 958 is intended for the purpose ofcreating an appropriate amount of compression between plunger buttonassembly 951 and frusto-conical portion 953 by allowing a spring 959 inplunger button assembly 951 to bend to a desired extent by a plungerbutton capture spacer 960. The thinner the spacer 958, the greater thebending of spring 959 in plunger button assembly 951, consequentlycreating greater compression between plunger button assembly 951 andfrusto-conical portion 953.

[0065] From output plenum 938, fluid flows through grooves/channels 961(FIG. 18) formed into orifice plate 952 and into opening 954. The amountof fluid flowing into opening 954 depends on the positioning of plungerbutton assembly 951 in relation to orifice plate 952. As the attractiveforce to plunger button assembly 951, which is created by the magneticflux, increases, plunger button assembly 951 is moved away from orificeplate 952, thereby increasing the amount of fluid flowing into opening954. However, as the force decreases, spring 959 pushes plunger buttonassembly 951 towards orifice plate 952, thereby decreasing the fluidflow into opening 954. The regulated fluid from opening 954 then flowsthrough a fluid output channel 955 and exits from output port 956.

[0066] Although the invention has been described with reference toparticular embodiments, the description is only an example of theinvention's application and should not be taken as a limitation. Forexample, the above description describes magnetic flux traveling fromthe input to the output. However, the magnetic flux can also travel fromthe output to the input along the direction of the bypass assembly forcontrolling the fluid flow. The concepts described above can then bemodified to open or close the path of the fluid in response to thepresence of the magnetic flux. Consequently, various adaptations andcombinations of features of the embodiments disclosed are within thescope of the invention as defined by the following claims.

I claim:
 1. A mass flow controller, comprising: a flow input portlocated on a lower end of the controller; a flow output port located onthe lower end of the controller; a sensor unit in fluid connection withthe input port and the output port; a first channel for carrying a firstamount of fluid from the input port to the output port; a second channelfor carrying a second amount of fluid through the sensor unit, whereinthe second amount is less than the first amount; an orifice assemblycoupled to the output port, wherein the orifice assembly has at leastone orifice opening; and a magnetic field generator coupled between theorifice assembly and the sensor, wherein the magnetic field generator,in response to the sensor unit, generates a magnetic flux in a directionfrom the sensor unit to the orifice assembly to allow flow through theat least one orifice opening.
 2. The mass flow controller of claim 1,wherein the flow direction through the sensor unit is approximatelyperpendicular to the flow direction of the magnetic flux.
 3. The massflow controller of claim 1, further comprising a bypass assembly coupledbetween the sensor unit and the orifice assembly, wherein the bypassassembly comprises grooves to allow fluid to flow through.
 4. The massflow controller of claim 3, further comprising a spring-biased sealingmechanism coupled between the bypass assembly and the orifice assemblyand moveable along the flow direction.
 5. The mass flow controller ofclaim 4, wherein the orifice assembly comprises an orifice plate, andwherein the sealing mechanism is located between the bypass assembly andthe orifice plate.
 6. The mass flow controller of claim 4, wherein thesealing mechanism has openings to allow flow to the orifice plate. 7.The mass flow controller of claim 1, wherein the at least one orificeopening is a central hole.
 8. The mass flow controller of claim 4,wherein the spring-biased sealing mechanism seals the at least oneorifice opening when no magnetic flux is generated.
 9. The mass flowcontroller of claim 1, wherein the magnetic field generator comprises: asolenoid core; and a solenoid coil surrounding the solenoid core,wherein the solenoid core comprises a ferromagnetic material.
 10. Themass flow controller of claim 3, wherein the magnetic flux travelsthrough the bypass assembly.
 11. A mass flow controller, comprising: aninput port; a first input channel in fluid connection with the inputport; a second input channel in fluid connection with the first inputchannel, wherein the second input channel is smaller than the firstinput channel; a sensor unit in fluid connection with the second inputchannel; a magnetic field generator located between the sensor unit andthe input port; an output channel in fluid connection with the sensorunit; an output port in fluid connection with the output channel; and anorifice assembly located between the magnetic field generator and theoutput port, wherein the orifice assembly has at least one opening and,in response to magnetic flux generated by the generator from the sensorunit to the output port, the at least one opening opens to allow fluidflow to the output port.
 12. The mass flow controller of claim 11,wherein the magnetic field generator is located approximately parallelto and at least partially overlaps the first channel.
 13. The mass flowcontroller of claim 11, further comprising a bypass assembly locatedbetween the sensor unit and the output port.
 14. The mass flowcontroller of claim 11, wherein the at least one opening is sealed whenno magnetic flux is generated by the magnetic field generator.
 15. Themass flow controller of claim 11, wherein fluid flow through the sensorunit is approximately perpendicular to the flow direction of themagnetic flux.
 16. The mass flow controller of claim 11, wherein theinput port and the output port are located at the same end of the massflow controller.
 17. The mass flow controller of claim 13, furthercomprising a spring-biased sealing mechanism located between the bypassassembly and the orifice assembly.
 18. The mass flow controller of claim17, wherein the sealing mechanism comprises a ferromagnetic material.19. A method for controlling flow through a mass flow controller havinga flow input, a flow output, a sensor unit, and a bypass assembly and amagnetic field generator coupled between the sensor unit and the flowinput and output, the method comprising: introducing a fluid into theflow input; generating an electrical signal, dependent upon a desiredflow rate and a measured flow rate, to the magnetic field generator;generating a magnetic flux, dependent on the electrical signal,traveling in a direction approximately parallel to the bypass assembly;in response to the magnetic flux, adjusting the position of a sealingmechanism relative to an orifice to adjust the flow rate through theorifice; and delivering the fluid out from the flow output in adirection opposite of the fluid introduction.
 20. The method of claim19, further comprising directing a flow through the sensor unitapproximately perpendicular to the flow direction through the bypassassembly.
 21. The method of claim 19, wherein the adjustment of thesealing mechanism is in a direction approximately parallel to the flowdirection.
 22. The method of claim 19, wherein in the absence of themagnetic flux, the sealing mechanism seals the orifice.
 23. The methodof claim 19, wherein the magnetic flux travels through the bypassassembly to pull the sealing mechanism away from the orifice.
 24. Themethod of claim 19, wherein the magnetic flux travels through the bypassassembly.